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    Specify the command to be executed on the controller before Jenkins
    starts using the agent. This executes in JENKINS_HOME.

    <p>
    Any non-zero exit code will prevent the command to prepare the agent from being executed.

    <p>
    Commands typed in here are executed as a shell script (by using the shell you specified
    in the system config page), but if you need to use a different interpreter,
    start with "#!" and it'll execute the script with your interpreter of the choice.

    <p>
    The script has the environment variables NODE_TO_SETUP_NAME and NODE_TO_SETUP_LABELS at its disposition.
    They are set to the NODE_NAME and NODE_LABELS of the agent which is being launched.
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